Okay, let me take a shot at it:
Would it be possible for the area of the keys (home, back, send, and end) to shrink? So e.g. the key only works if it's pressed at the corner (like in the picture)? And the rest of it would be for the d-pad?
*(translated by google and edited to make a little clearer)
No, I don't think so. I would like that too, but as those are physical buttons with mechanisms underneath, I would doubt that's possible.
Maybe it would be possible if you use the capacitive touchpad, and map it accordingly. But then it would be a hassle since just touching it would "activate" the key. So if I take the phone out of the pocket and I brush on the End key, the call would be rejected.
Or maybe someone else has another idea...